timedata: make it possible to reset the state

Add a new function `TestOnlyResetTimeData()` which would reset the
internal state used by `GetTimeOffset()`, `GetAdjustedTime()` and
`AddTimeData()`.

This is needed so that unit tests that call `AddTimeData()` can restore
the state in order not to confuse other tests that rely on it.

Currently `timedata_tests/addtimedata` is the only test that modifies
the state (via `AddTimeData()`) and also the only test that relies on
that state.

src/test/timedata_tests.cpp

@@ -96,9 +96,10 @@ BOOST_AUTO_TEST_CASE(addtimedata)
     // not to fix this because it prevents possible attacks. See the comment in AddTimeData() or issue #4521
     // for a more detailed explanation.
     MultiAddTimeData(2, 100); // filter median is 100 now, but nTimeOffset will not change
+    // We want this test to end with nTimeOffset==0, otherwise subsequent tests of the suite will fail.
     BOOST_CHECK_EQUAL(GetTimeOffset(), 0);
 
-    // We want this test to end with nTimeOffset==0, otherwise subsequent tests of the suite will fail.
+    TestOnlyResetTimeData();
 }
 
 BOOST_AUTO_TEST_SUITE_END()

src/timedata.cpp

@@ -39,18 +39,20 @@ int64_t GetAdjustedTime()
 
 #define BITCOIN_TIMEDATA_MAX_SAMPLES 200
 
+static std::set<CNetAddr> setKnown;
+static CMedianFilter<int64_t> vTimeOffsets(BITCOIN_TIMEDATA_MAX_SAMPLES, 0);
+static bool fDone;
+
 void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample)
 {
     LOCK(g_timeoffset_mutex);
     // Ignore duplicates
-    static std::set<CNetAddr> setKnown;
     if (setKnown.size() == BITCOIN_TIMEDATA_MAX_SAMPLES)
         return;
     if (!setKnown.insert(ip).second)
         return;
 
     // Add data
-    static CMedianFilter<int64_t> vTimeOffsets(BITCOIN_TIMEDATA_MAX_SAMPLES, 0);
     vTimeOffsets.input(nOffsetSample);
     LogPrint(BCLog::NET, "added time data, samples %d, offset %+d (%+d minutes)\n", vTimeOffsets.size(), nOffsetSample, nOffsetSample / 60);
 
@@ -81,7 +83,6 @@ void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample)
         } else {
             nTimeOffset = 0;
 
-            static bool fDone;
             if (!fDone) {
                 // If nobody has a time different than ours but within 5 minutes of ours, give a warning
                 bool fMatch = false;
@@ -108,3 +109,12 @@ void AddTimeData(const CNetAddr& ip, int64_t nOffsetSample)
         }
     }
 }
+
+void TestOnlyResetTimeData()
+{
+    LOCK(g_timeoffset_mutex);
+    nTimeOffset = 0;
+    setKnown.clear();
+    vTimeOffsets = CMedianFilter<int64_t>(BITCOIN_TIMEDATA_MAX_SAMPLES, 0);
+    fDone = false;
+}

src/timedata.h

@@ -75,4 +75,9 @@ int64_t GetTimeOffset();
 int64_t GetAdjustedTime();
 void AddTimeData(const CNetAddr& ip, int64_t nTime);
 
+/**
+ * Reset the internal state of GetTimeOffset(), GetAdjustedTime() and AddTimeData().
+ */
+void TestOnlyResetTimeData();
+
 #endif // BITCOIN_TIMEDATA_H